Wellbores for producing oil, gas or other fluids from subsurface formations are often drilled in stages. For example, a wellbore may first be drilled with a drill string and a first drill bit having a relatively large diameter. At a desired depth for a first portion of the wellbore, the drill string and drill bit are removed from the wellbore. A tubular member of smaller diameter, often referred to as a casing or a casing string, may then be placed in the first portion of the wellbore. An annulus formed between the inside diameter of the wellbore and the outside diameter of the casing string is generally filled with cement. The cement provides support for the casing and isolates downhole formations or subterranean strata from each other. Many oil and gas wells are completed with a relatively large diameter casing at the well surface and a smaller diameter casing extending from the large diameter casing in a telescoping or stair step pattern from the well surface to a desired downhole location. One or more strings of production tubing along with appropriate well completion tools may be installed within the casing strings for use in producing formation fluids from one or more downhole locations.
For very deep wells and very long wells, sometimes referred to as extended reach wells (20,000 feet or greater), there may be three or four changes in casing diameter from the well surface to total depth of the wellbore. Each change in casing diameter often results in decreasing the diameter of production tubing used to produce formation fluids from a desired downhole location. Changes in casing diameter associated with deep wells and/or long wells result in significantly increased drilling and completion costs for associated wells.
Steel, an alloy of iron, is typically made by oxidizing excess carbon and other impurities from molten pig iron. Steel alloys may be produced by injecting substantially pure oxygen into molten iron. Steel alloys may also be produced in electric furnaces which use iron ore as a source of oxygen to remove excess carbon.
Steel alloys typically include relatively high percentages of iron (Fe) and one or more nonmetallic elements. Carbon (C) is one of the most common nonmetallic elements associate with steel alloys. One or more metal elements in addition to iron may be included in many steel alloys. For example, some steel alloys may contain chromium (Cr) and nickel (Ni). Such alloys may sometimes be referred to as “stainless steel.” Oil country tubular goods are frequently formed from steel alloys which have been quenched and tempered to produce desired characteristics such as yield strength and ductility. Such steel alloys often have 90% to 95% or greater tempered martensite by volume of the steel alloy.
Martensite may generally be described as a solid solution of iron which typically contains one percent or less of carbon. Martensite is often a chief constituent of hardened carbon tool steels. Martensite may be formed by heating steel alloys and then quenching them in cold water. Martensite is sometimes difficult to obtain during quenching of low carbon steel alloys and very low carbon steel alloys. A wide variety of commercial techniques and procedures have been developed for use in satisfactorily quenching low carbon steel allows and very low carbon steel alloys with desired martensite concentrations.
A number of oil and gas wells have been completed using solid, expandable casings and other types of solid, expandable tubular members. Electric resistant welded (ERW) pipe has been used to form such casings. Examples of steel alloys and steel compositions which have previously been used to manufacture solid, expandable casings include quenched and tempered steel alloys with carbon concentrations between approximately 0.22% and 0.25%. The yield strength of such steel alloys may range between approximately 70,000 and 80,000 pounds per square inch with an upper limit of approximately 95,000 pounds per square inch. Casing formed from such steel alloys may be radially expanded up to approximately twenty-five percent (25%) within a wellbore. Average radial expansion for casing formed from such steel alloys may be approximately fifteen percent (15%).